Advanced Optics and Light management
A key strategy to reduce the economic costs of next generation photovoltaics is to enhance their potential to absorb incident solar radiation and transform it into electrical energy. Our group designs, develops and prototypes novel optical concepts for improved light incoupling at the front side of the solar module as well as light-trapping concepts that allow all incident light to be guided and absorbed more efficiently in the solar cell. As we detailed in a perspective paper in 2019 , light management concepts are also key to high-efficiency perovskite-based tandem photovoltaics.
Tailored light-matter interaction in nanophotonic perovskite solar cells
Nanophotonic electrodes and nanopatterned perovskite solar cells make use of the full potential of periodic or quasiperiodic 3D-nanostructured materials to control the spectral and angular light propagation, light incoupling, and light outcoupling   . In a recent study, we reported on the simulation-based design, implementation, and prototyping of nanophotonic front electrodes for perovskite/c-Si tandem solar cells, leading to a significant improvement in the power conversion efficiency .
Figure 1: Photograph of the front side of prototype perovskite solar cells with nanophotonic front electrodes. The five areas with decreased brightness indicate the regions of the nanopatterns of the ITO front electrode. The light diffreaction at the nanopatterned electrodes is apparent by a colored haze.
Guiding light around interconnection lines, contact fingers, and dead areas
Invisibility cloaking by freeform surfaces is a new concept to guide incident light for all angles of incidence away from inactive areas of solar cells. In collaboration with our partners, we realized a freeform surface that allows cloaking of interconnection lines and finger grids at the front side of solar cells and modules.   
Figure 2: Schematic illustration of the working principle of the invisibility cloak which guides sunlight past the contacts to the active surface area of the solar cell. (Graphics: Martin Schumann, APH, KIT).
What does nature teach us for light management in solar cells?
Nature’s evolution provides a multitude of solutions to scientific and technological challenges. In a study form 2017, we applied the unique texture of viola petals for improved light harvesting in solar cells . Inspired from these observations, we derived artificial conical microtextures for front-side coatings of solar modules that yielded further improved light management   . In addition to optical improvements, these microtextures even feature a superhydrophobic surface that induces a self-cleaning effect .
Figure 3: Texture of the viola flower enhances the external quantum efficiency (EQE) of a silicon solar cell. The reduced reflection of incident light is clearly visible by the decreased brightness. The viola texture consists of micron-scale cones.